Starting in 1970, environmental laws began to regulate landfills. But some of the old landfills built before then have left a legacy of problems-not the least of which are chemicals that can seep out and pollute water supplies and surrounding soils.

In Lake County, two such old landfill sites are leaking chemicals, and state and federal environmental authorities are grappling with the tricky problem of repairing them.

Landfill No. 7 at the former Ft. Sheridan Army base was used in the 1940s, and again in the 1960s and 1970s, for household, hospital and industrial wastes.

The military stopped using it in July 1979, but now state environmental officials say that it appears to be leaking iron-tainted liquid into a storm drain that runs under the landfill and empties into Lake Michigan.

The second problem dump is the Yeoman Creek Landfill site in Waukegan.

The twin landfills there, used from 1958 to 1969 for household and industrial garbage, are believed to be leaking polychlorinated biphenyls (PCBs) and other chemicals into the small tributary that flows next to and through part of the landfills. That creek empties into the Waukegan River, which flows into Lake Michigan.

Fixing the leaky landfills will take some doing, environmental officials say, in large part because water flows through them, picking up chemicals and carrying them out of the landfill into the environment.

"Whenever there is water, whether a creek, river or a lake, that makes the fix a little more difficult," said Greg Michaud, a spokesman for the Illinois Environmental Protection Agency.

But without repairs, the landfills will continue to leak chemicals into Lake Michigan, a source of drinking water for many communities.

Modern landfills have high-tech impermeable liners surrounding the bottoms and sides to keep liquids from escaping. They have secure caps of soil alone or soil used with a synthetic material that keep out rainwater and snow, and sophisticated gas collection systems.

"New landfills have a bottom cover, a leachate collection system and a top cover," said Richard Boice, Yeoman Creek site project manager for the U.S. Environmental Protection Agency.

"There should be no leakage," Boice said. "If there is, one of those systems or more have failed."

Restoring or adding some of those systems to aging landfills is the goal of environmental officials who want to keep the garbage and the chemicals contained.

When looking at repair options for a leaking landfill, one of the first things officials consider is how to keep out water. Besides washing chemicals out into the surrounding environment, water can mix with decomposing garbage and create a rotting, smelly brew.

Water penetration is one thing that the two Lake County landfill sites have in common. So controlling water intake and leachate out of the landfills will be important, say environmental officials.

Officials already know, for example, that one of the problems at Yeoman Creek that needs to be fixed is an inadequate cover of topsoil that allows water to flow into and through the landfill carrying pollutants into the environment.

"They did put some soil on top," said the U.S. EPA's Boice, "but only enough to prevent rodents and odors. It was not made to promote runoff."

Potential solutions that will be considered for the county's aging landfills will include replacing the top cover with an impermeable cap.

Other options include adding a leachate collection system that gathers and treats the liquid that seeps out. That is done by drilling tunnels through the core of the landfill or digging trenches around the perimeter of the landfill in order to capture leachate, as well as gases produced by decomposing garbage.

As for landfills such as Yeoman Creek's that do not have inner liners, it is next to impossible to install one without excavating the garbage that is already there. And excavation of garbage is something that is rarely done for any reason.

"There are major problems with excavation," said the Illinois EPA's Michaud. Not the least of which is accidentally releasing landfill contaminants further into air, water or surrounding soil.

The U.S. Army Corps of Engineers is just now beginning to study the problem at Ft. Sheridan, but it hopes to decide on a remedy by the end of next year.

The Yeoman Creek Landfill site, which includes the Yeoman Creek Landfill and the adjacent Edwards Field Landfill, was declared a Superfund site-meaning it is among the most severely polluted properties in the nation-by the U.S. EPA in 1986.

State and federal officials have been studying the extent of the pollution since 1990, and the study is expected to be finished in a few months. Once the study is finished, solutions will be selected by the state and federal EPAs.